I got this question from a recent mom of 2:
Man, does this ever bring back memories. Not all kids do this, but many do. My twin boys made INSANE noises in their sleep. I remember calling one "race car" and the other "sqealler". The sounds are alien. They're like nothing you've heard before if you haven't been around newborn babies sleeping and I for one couldn't sleep through them either. I had all intentions to leave the crib in our bedroom (my boys were in one crib together for a while) for at least the first few months. But I was getting no sleep at all with them in there. In my case, they both started sleeping more quietly (or at least the sounds weren't as high-pitched and strange) around the 3-month mark. I've heard similar stories from loads of moms, but as far as I know, there are no empirical studies in developmental science that have marked a precise age at which these alien calls subside. Nor is there any consensus on what causes them.
In terms of what to do, I don't think there's much to do in terms of getting him to stop the noises. And as I've mentioned recently, any changes in his sleeping SCHEDULE should probably not be made this early in his life. So, the choices I see for you are all about his location: (1) try putting the baby in a crib in another room, if that's what you're eventually planning on doing anyway and TURN THE MONITOR OFF (since this is your second, I'm sure you know you'll wake up from a baby's cry without the need of any amplification if his crib is at a reasonable distance from you), (2) try putting the baby in a co-sleeper or bassinet next to your bed — maybe if he isn't right next to your body or ears, you could get used to the sounds easier, or (3) grin and bear it for the time being, if co-sleeping is your priority. You may very well get used to the sounds and stop waking up so frequently from them when your nervous system has stopped reacting to them so dramatically.
Any pediatrician or knowledgeable parent out there know the biological underpinnings of these cries? What have others done in similar situations? If you're not currently in that early stage, can anyone even remember back to those early weeks?